RECYCLING OF STRATEGIC METALS FROM INDUSTRIAL SLAG BY A HYDROMETALLURGICAL AND PYROMETALLURGICAL PROCESS

Tin slag may contain up to 25% of (Nb + Ta)2O5. Tantalum and niobium are used in advanced technologies. Classical methods for the extraction of these elements are based on the full dissolution of these slags by HF or (HF + H2SO4.). This leads to high reagent consumption, due to presence of Si, Fe, Mn, Ca, Al oxides, and the production of toxic wastes. This paper describes a new approach for the characterization and extraction of these metals based on a combined hydro- and pyrometallurgical process. The planning of successive alkaline and acid leaching of this slag based on the ''pseudo-structure'' of these amorphous materials permits a selective dissolution of the economic metals, a lower consumption of chemical reagents, especially HF, less toxic residues and a high grade concentrate (up to 60% of pentoxide of tantalum and niobium) with a satisfactory recovery rate (about 85%). These concentrates are subjected to a subsequent selective carbochlorination, at temperatures lower than 500-degrees-C, leading to full extraction of niobium compounds at 300-degrees-C and that of tantalum at 500-degrees-C.